Thank heaven for the massive marches across the country by those favoring illegal immigrants. These marches revealed the ugly truth behind the fog of pious words and clever political spin from the media and from both Democrats and Republicans in Washington.

"Guest workers"? Did any of the strident speakers, with their in-your-face bombast in Spanish, sound like guests? Did they sound like people who wanted to become Americans?

Were they even asking for amnesty? They didn't sound like they were asking for anything. They sounded like they were telling. Demanding. Threatening.

Somebody must have told them that their Mexican flags that dominated the earlier marches were not making a good impression on television, so they started flying American flags. But such cosmetic changes did not keep the ugly reality from coming through in their hostile speeches.

These were not the speeches of people who wanted to join American society but people who wanted their own turf on American soil -- in disregard and defiance of what American citizens want.

Europe has already been through this "guest worker" policy that we are being urged to follow. They have learned the hard way what it means to have a growing foreign population in their midst -- a population that insists on remaining foreign and hostile to the culture, values and people around them.

Some European countries have learned this lesson at the cost of riots and bloodshed in the streets and lives lost in terrorist attacks. Others have only had to contend with national polarization -- thus far -- but polarization is not a small thing.

In this country, however, there are still people who refuse to learn any lesson at all. Some business interests see only an opportunity to get cheap labor. Some intellectuals see only abstract principles about abstract people crossing an abstract border.

Some tell us loftily that earlier generations of immigrants who were once thought to be unassimilable turned out over time to become as American as anyone else and patriotic citizens.

That might well be true of immigrants from Mexico, both legal and illegal, if the circumstances of today were the same as the circumstances during an earlier era of immigration from Europe. But circumstances are not the same -- and those circumstances are not going to become the same by pretending that they are.

The ugly display of grievance-mongering bombast at the illegal immigrant marches is just one of those circumstances that are not the same as in an earlier era.

When people came here from Europe, they came here to become Americans. There was no prouder title for them.

American generals of German ancestry led the fight against Germany in both World Wars. The Irish "Fighting 69th" earned its fame on the battlefields of the First World War and Japanese American fighting units were among the most highly decorated in World War II. They proved they were Americans.

The underlying tragedy of the present situation is that it is doubtful whether the activist loudmouths, who were too contemptuous of this country to even speak its language while demanding its benefits, represent most immigrants from Mexico.

Both legal and illegal immigrants have come here primarily to work and make a better life for themselves and their families. But a country requires more than workers. It requires people who are citizens not only in name but in commitment.

Americanization did not happen automatically in earlier times and it will not happen automatically today. Immigrants in an earlier era had leaders and organizations actively working to transform them into Americans -- the Catholic Church with the Irish and numerous organizations among the Jews, for example.

Today's immigrant activists and the politicians who kowtow to them have just the opposite agenda, to keep foreigners foreign and to make other Americans accept and adjust to that. It will be a national tragedy if they succeed.

Just what problem will amnesty solve? Illegal aliens will benefit and politicians will benefit by sweeping the illegality under the rug by making it legal. But how will American citizens benefit? America can lose big time.

Thomas Sowell is a senior fellow at the Hoover Institution.

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